This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A central goal of visual neuroscience is to understand how neural activity gives rise to perceptual experience. Color vision is a premier platform for achieving this goal. In color vision, well-characterized aspects of perception can be accounted for completely by well-understood properties of the peripheral receptors. Our deep understanding of the output and input of the color vision system stands in stark contrast to how little we know about the neural machinery in between;color processing in the cerebral cortex is still poorly understood. To discover the contribution that the primary visual cortex makes to color vision, we record from single neurons in animals viewing a computer monitor. We characterize each neuron that we study by presenting a rapid sequence of randomly generated colorful patterns. By chance, some of these patterns excite the neuron, and by analyzing these patterns exclusively, we gain valuable information about the role of that neuron plays in processing visual information. This characterization also allows us to configure the display for behavioral tasks that probe the perceptual consequences of this processing. In one task, we simultaneously probe the sensitivity of the neuron and animal to faint colored lights. Results from this experiment tell us which neurons are sufficiently sensitive to mediate color vision and how their signals must be pooled to support color detection. In another task, we measure the effect of background color on the neurons and on the animal's judgments of color similarity. Results from this experiment indicate whether spatial contrast effects in color vision are mediated by processing at the level of primary visual cortex, or are the result of processing at higher levels of the visual system.